Moves ATIS carrier/broadcast loop, TTS audio caching, METAR fallback,
and the background airport-data refresh scheduler out of live-atc.vue.
Also extracts the pmLog debug logger to shared/utils/pmLog.ts since it
has no Vue/component dependency and multiple composables need it —
threading it through every composable's parameter list would've been
worse than giving it one shared home. Verified via typecheck plus a
browser mount/redirect smoke test.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
